1. Field of the Invention
The present invention relates to a solid state image pickup device and to a camera, and particularly to those suitably used in a CMOS area sensor.
2. Related Background Art
In recent years, a CMOS area sensor having a photodiode and a MOS transistor integrated into one-chip has been used for a solid-state image sensing device. The CMOS area sensor has advantages of consuming a less electric power, needing a lower drive power and working in a higher speed than a CCD. Accordingly, the CMOS area sensor is expected to grow in demand in future.
For this reason, it has been proposed to enlarge a dynamic range of a solid-state image sensing device, by using such a CMOS area sensor.
The solid-state image sensing device includes a plurality of pixels having, for instance; a photodiode; a floating diffusion region (which may be abbreviated as FD, hereafter as needed); a first transfer transistor for transferring carriers from the above described photodiode to the above described floating diffusion region; an additional capacitor for accumulating the carriers overflown from the above described photodiode; a second transfer transistor for transferring the carriers from the above described additional capacitor to the above described floating diffusion region; and a reset transistor for resetting the above described floating diffusion region and the above described additional capacitor, to a predetermined potential. A certain solid state image pickup device has the CMOS area sensor having the pixels configured into a matrix shape (see a non-patent literature: Shigetoshi Sugawa, et al. “A 100 db Dynamic Range CMOS Image Sensor Using a lateral Overflow Integration Capacitor”, ISSCC 2005/SESSION19/IMAGES/19.4, DIGEST OF TECHNICAL PAPERS, 2005 IEEE International Solid-State Circuit Conference, Feb. 8, 2005, P352-353, 603).
The non-patent literature describes a technology of accumulating carriers overflown from the above described photodiode by using the above described additional capacitor, and transferring the accumulated carriers to the above described floating diffusion region with the use of the above described second transfer transistor. Thereby, the technology can form a pixel signal through using the carriers accumulated in the above described additional capacitor and the carriers accumulated in the above described photodiode, and consequently can enlarge a dynamic range of a CMOS area sensor. In the technology, as the above described additional capacitor increases its capacitance value, it can accumulate more carriers, and can more enlarge the dynamic range of the CMOS area sensor.
However, in the above described conventional technology, the capacitance of the above described additional capacitor is not concretely considered. Therefore, the above described additional capacitor has a possibility of being upsized with the increase of the capacitance value of the above described additional capacitor. The above described additional capacitor is formed in a pixel, so that the upsizing of the above described additional capacitor may lead to the upsizing of the pixel.
The present invention is designed with respect to the above problems, and is directed at providing a solid state image pickup device which realizes the enlargement of a dynamic range and the minimization of a size of a pixel, and at providing a camera using the solid state image pickup device.